Objective  Rational cutting can promote the growth of trees and increase the productivity of stands. It is of no important practical significance to determine cutting with the aim of optimizing the spatial structure of stands. In this study, the natural forest composed of different tree species in Changbai Mountain of northeastern China was taken as the object, and the combination weight method of AHP-CRITIC was adopted to construct single tree cutting index, in order to provide a new guiding tool for the selection of natural forest cutting wood in this area.

  Method  In this paper, the monitoring data of 4 natural forest fixed samples with different dominant tree species were adopted, four spatial structure indexes, including mingling degrees (M), uniform angle index (W), dominance degrees (U) and Hegyi competition index (CI) were used, and the individual tree felling index (F_i) was constructed according to AHP-CRITIC combination weight method. The spatial structure changes of stand before and after cutting simulation with different intensities were analyzed.

  Result  After cutting, the spatial structure of the four sample plots was optimized to a certain extent: the mingling degrees increased, the degree of tree size differentiation decreased, the horizontal distribution pattern of stand tended to random distribution, and the pressure of stand competition was greatly relieved. The competition index showed a trend of continuous decline with the increase of cutting intensity. Under 30% cutting intensity, the competition index decreased by 24.80%−34.88% at most, the size ratio decreased by 24.97% at most, and the mixing degree increased by 12.76% at the highest. The felled trees were mainly concentrated in the area with high density, and most of the felled trees were small and medium-sized in DBH.

  Conclusion  Through comparative analysis of data before and after simulated cutting, it is proved that for natural pure forest, moderately increasing cutting intensity can better regulate the spatial structure of the stand, while for natural mixed forest, relatively low intensity cutting can optimize its overall structure and maintain a higher degree of tree species mixing. At the same time, the research proves that it is reasonable for AHP-CRITIC combination weight method to construct cutting index, which basically realizes the optimization and adjustment of natural forest stand structure in Changbai Mountain, and can provide technical support for reasonable selection of cutting wood and reasonable management of forest.